Time-division duplexing (tdd) in distributed communications systems, including distributed antenna systems (dass)

ABSTRACT

Time-division duplexing (TDD) in distributed communications systems, including distributed antenna systems (DASs) is disclosed. In one embodiment, a control circuit is provided and configured to control the TDD transmit mode of a DAS to control the allocation of time slots for uplink and downlink communications signal distribution in respective uplink path(s) and downlink path(s). The control circuit includes separate power detectors configured to detect either a transmit power level in a downlink path or a receive power level in an uplink path. If the transmit power detected in the downlink path is greater than receive power detected in the uplink path, the control circuit switches the TDD transmit mode to the downlink direction. In this manner, the control circuit does not have to control the TDD transmit mode based solely on detected power in the downlink path, where a directional coupler may leak uplink power in the downlink path.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/962,338 filed on Dec. 8, 2015, which is a continuation ofInternational Application No. PCT/IL14/050526, filed on Jun. 11, 2014,which claims the benefit of priority to U.S. Provisional Application No.61/834,075, filed on Jun. 12, 2013, all applications being incorporatedherein by reference.

BACKGROUND

The technology of the disclosure relates to distributed antenna systemsconfigured to provide communications signals over a communicationsmedium to and from one or more remote units for communicating withclient devices.

No admission is made that any reference cited herein constitutes priorart. Applicant expressly reserves the right to challenge the accuracyand pertinency of any cited documents.

Distributed antenna systems (DASs) are effective when deployed insidebuildings or other environments where client devices may not otherwisereceive radio-frequency (RF) signals from a base station or othersource. DASs can be used to provide coverage for applications such aspublic safety, cellular telephony, wireless local access networks(LANs), location tracking, and medical telemetry inside buildings andover campuses. A typical DAS establishes a number of RF antenna coverageareas, also referred to as “antenna coverage areas.” The antennacoverage areas are formed by remotely distributed antenna units (RAUs),which are sometimes referred to as remote units (RUs). A number ofremote units are arranged to create an array of relatively small antennacoverage areas, with each RAU typically accommodating a small number ofwireless client device users. This arrangement thus provides a uniformhigh quality signal and high throughput for wireless users.

Time-division duplexing (TDD) refers to duplex communication links whereuplink is separated from downlink by the allocation of different timeslots in the same frequency band. In TDD, users are allocated time slotsfor uplink and downlink transmission. When a DAS serves TDD wirelessprotocols, it must identify whether a radio source is transmitting(i.e., is in TDD Tx mode) or receiving (TDD Rx mode) and toggle itstransmit/receive circuits accordingly. Conventional WiFi systems usingTDD, for example, determine whether to toggle to TDD transmit (Tx) modeor stay in TDD receive (Rx) mode based on the output of a power detectorthat senses the power level at the radio port side of the DAS.

In this regard, FIG. 1 illustrates one such conventional system coupledto a radio source 10, such as a base station or transceiver. In FIG. 1,a TDD DAS head end 12 of a DAS 14 is provided. The TDD DAS head end 12may also be a TDD repeater. The TDD DAS head end 12 receives TDDcommunications signals 16 in the form of TDD downlink communicationssignals 16D from the radio source 10 and provides TDD uplinkcommunication signals 16U to the radio source 10. In the TDD DAS headend 12, a power detector 18 senses the power level of TDD communicationssignals 16 at the radio port side of the TDD DAS head end 12 todetermine whether to toggle to TDD transmit (Tx) mode or stay in TDDreceive (Rx) mode. The default status of the TDD DAS head end 12 is TDDreceive (Rx) mode, where the DAS 14 is set to transfer signals in theuplink direction. When the power detector 18 detects power of the TDDcommunication signals 16 above a certain threshold, the assumption isthat the power is sourced from TDD downlink communications signals 16Dreceived from the radio source 10. This is because the power of the TDDdownlink communications signal 16D is typically lower (e.g., 30-40 dBlower) than the power of the TDD uplink communications signals 16U dueto loss. In response to the power detector 18 detecting power of the TDDcommunications signals 16 above a certain threshold, the TDD DAS headend 12 toggles input switch 20 and antenna switch 22 to TDD transmit(Tx) mode, where its circuits are set to transfer signals in thedownlink direction.

One of the drawbacks of the DAS 14 in FIG. 1 is that the power generatedby a receive (Rx) Amp 24 can leak through the directional coupler 26 tothe power detector 18. For example, the directional coupler 26 may onlyhave a directivity of up to 15 or 20 dB, but the difference in powerbetween the TDD downlink communications signals 16D and the TDD uplinkcommunications signals 16U may be greater than the directivitycapability of the directional coupler 26. If power leaking from thereceive (Rx) Amp 24 is high enough, it can cause the level comparator 28to toggle the input switch 20 and the antenna switch 22 from TDD receive(Rx) mode to TDD transmit (Tx) mode even when the radio source 10 is nottransmitting.

SUMMARY

Embodiments disclosed in the detailed description include time-divisionduplexing (TDD) in distributed communications systems, includingdistributed antenna systems (DASs). Related circuits, systems, andmethods are also disclosed. In one embodiment, a control circuit isprovided in a TDD distributed communications system in the form of a TDDDAS, for example a TDD DAS head end. The control circuit is configuredto control the TDD transmit mode of the DAS to control the allocation oftime slots for uplink and downlink communications signal distribution ina respective uplink path(s) and downlink path(s). The control circuitincludes separate power detectors configured to detect either a transmitpower level in the downlink path or a receive power level in the uplinkpath. In this manner, the transmit power in the downlink path can bedetected separately form the receive power in the uplink path. If thetransmit power detected by a power detector in the downlink path isgreater than the receive power detected by another power detector in theuplink path, the TDD transmit mode is switched to the downlinkdirection. In this manner, the control circuit does not have to rely onan assumption that the TDD transmit mode should be in uplink directionbased solely on detected power in the downlink path, where a directionalcoupler may leak uplink power to the downlink path.

One embodiment of the disclosure relates to a control circuit controlsswitching in a system supporting time-division duplexing (TDD). Thecontrol circuit comprises a first power detector configured to determinea first power level from a radio source, a second power detectorconfigured to determine a second power level in an uplink path, and areceive/transmit comparator. The receive/transmit comparator is coupledto the first power detector and to the second power detector, andcompares the first power level to the second power level to provide anindication that the system should be switched to a TDD transmit modewhen the first power level exceeds the second power level.

An additional embodiment of the disclosure relates to a distributedcommunication system capable of supporting time-division duplexing (TDD)comprises a central unit configured to receive a plurality of downlinksignals from at least one radio source, a plurality of remote units eachconfigured to receive downlink signals from the central unit, and toreturn uplink signals to the central unit, and a control circuit forcontrolling TDD switching in the distributed communication system. Thecontrol circuit comprises a first power detector configured to determinea first power level from the at least one radio source, a second powerdetector configured to determine a second power level from an uplinkpath, and a receive/transmit comparator. The receive/transmit comparatoris coupled to the first power detector and to the second power detector,and compares the first power level to the second power level to providean indication that the distributed communication system should beswitched to a TDD transmit mode when the first power level exceeds thesecond power level.

The central units and remote units disclosed herein can be configured tosupport both RF communications services and digital data services. Thesecommunications services can be wired or wireless communications servicesthat are typically communicated wirelessly, but may be provided overnon-wireless medium (e.g., electrical conductor and/or optical fiber).The RF communications services and digital data services can be providedover any type of communications medium, including electrical conductorsand optical fiber to wireless client devices, such as remote units forexample. Examples of RF communications services are cellular servicesand radio communications services. Examples of digital data servicesinclude LAN using Ethernet, WLAN, WiMax, WiFi, Digital Subscriber Line(DSL), telephony, WCDMA, and LTE, which can support voice and data.Digital data signals can be provided over separate communications mediafor providing RF communications services, or over a commoncommunications medium with RF communications signals.

Additional features and advantages will be set forth in the detaileddescription which follows, and in part will be readily apparent to thoseskilled in the art from the description or recognized by practicing theembodiments as described in the written description and claims hereof,as well as the appended drawings.

It is to be understood that both foregoing general description and thefollowing detailed description are merely exemplary, and are intended toprovide an overview or framework to understand the nature and characterof the claims.

The accompanying drawings are included to provide a furtherunderstanding, and are incorporated into and constitute a part of thisspecification. The drawings illustrate one or more embodiment(s), andtogether with the description serve to explain principles and operationof the various embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a prior art implementation oftime-division duplexing (TDD);

FIG. 2 is a schematic diagram of an exemplary point to multi-pointoptical fiber-based distributed antenna system configured to distributeradio-frequency (RF) communications services and management services;

FIG. 3 illustrates a control circuit for controlling TDD switching in adistributed communication system according to one embodiment; and

FIG. 4 is a schematic diagram of a generalized representation of anexemplary computer system that can be included in or interface with anyof the exemplary distributed antenna systems and/or their componentsdescribed herein, wherein the exemplary computer system is adapted toexecute instructions from an exemplary computer-readable media.

DETAILED DESCRIPTION

Various embodiments will be further clarified by the following examples.

Before discussing a method of controlling time-division duplexing (TDD)switching in a distributed antenna system (DAS) with regard to FIG. 3, ageneral overview of a distributed communications system in the form of aDAS 30, in FIG. 2 is first provided. In this regard, the DAS 30 in FIG.2 includes a central unit 32. The central unit 32 is communicativelycoupled to one or more remote units 34(1)-34(N) via an optical fibercommunications medium 36. Thus, in this example, the DAS 30 is anoptical fiber-based distributed antenna system. However, the presentdisclosure is not limited to an optical fiber-based distributed antennasystem. Other communications mediums including twisted pair conductors(e.g., CAT 5/6/7 cable) and coaxial cables could be employed or employedin conjunction with optical fiber. The DAS 30 is configured todistribute RF communications signals and management signals. In thisregard, with regard to distribution of RF communications signals, thecentral unit 32 is configured to receive downlink communications signals38D, which may be downlink RF communications signals, from a RFcommunications network, such as through a base station 40 as an example.In this embodiment, the downlink communications signals 38D are downlinkelectrical communications signals 38D(E). The downlink electricalcommunications signals 38D(E), which may be downlink electrical RFcommunications signals, can be combined and converted to downlinkoptical communications signals 38D(0), which may be downlink optical RFcommunications signals, by the central unit 32 in this embodiment. Thedownlink optical communications signals 38D(0) are split and distributedby the central unit 32 over at least one downlink optical fiber 36D toeach of the remote units 34(1)-34(N) to provide one or more RFcommunications services to the client devices 42(1)-42(N) in wiredand/or wireless communication with the remote units 14(1)-14(N).

With continuing reference to FIG. 2, the remote units 34(1)-34(N)convert the downlink optical communications signals 38D(0) back todownlink electrical communications signals 38D(E), and communicate thedownlink electrical communications signals 38D(E) to one or more clientdevices 42(1)-42(N) to provide the one more RF communications servicesto the client devices 42(1)-42(N). The remote units 34(1)-34(N) can beconfigured to communicate through wired or wireless communications tothe client devices 42(1)-42(N). For example, if the remote units34(1)-34(N) are configured to be directly coupled to one client device42(1)-42(N) each, up to ‘N’ client devices 42(1)-42(N) may be connectedto the remote units 34(1)-34(N) in the DAS 30.

The remote units 34(1)-34(N) are also configured to receive uplinkcommunications signals 38U, which may be uplink RF communicationssignals, from the client devices 42(1)-42(N) to be distributed to thecentral unit 32 and the base station(s) 40. The uplink communicationssignals 38U are received from the client devices 42(1)-42(N) as uplinkelectrical communications signals 38U(E), which may be uplink electricalRF communications signals, which are combined and converted to uplinkoptical communications signals 38U(0), which may be uplink optical RFcommunications signals. The remote units 34(1)-34(N) distribute theuplink communications signals 38U(0) over at least one uplink opticalfiber 36U to the central unit 32. The central unit 32 receives andconverts the uplink optical communications signals 38U(0) back to uplinkelectrical communications signals 38U(E). The central unit 32 providesthe uplink electrical communications signals 38U(E) to the basestation(s) 40 to support the one or more RF communications services fromthe client devices 42(1)-42(N).

With continuing reference to FIG. 2, note that one common downlinkoptical fiber 36D may be provided between the central unit 32 and theremote units 34(1)-34(N) to carry downlink communications signals in apoint-to-multipoint communications configuration. Similarly, one commonuplink optical fiber 36U may be provided between the central unit 32 andthe remote units 34(1)-34(N) to carry uplink communications signals in apoint-to-multipoint communications configuration. Bi-directionalcommunications in the downlink and uplink directions are provided inthis embodiment of the DAS 30 in FIG. 2 by providing separate downlinkoptical fiber(s) 36D and uplink optical fiber(s) 36U in a respectivedownlink path 37D and uplink path 37U. Further, due to thepoint-to-multipoint configuration of the DAS 30 in FIG. 2, theembodiments disclosed provide time-division multiplexing (TDM) ofmanagement signals distributed in the DAS 30 to ensure that themanagement signals do not interfere with providing bi-directional,full-duplex communications. Alternatively, individual downlink opticalfibers 36D may be provided between the central unit 32 and each remoteunit 34(1)-34(N) to carry downlink communications signals in apoint-to-point communications configuration. The individual uplinkoptical fibers 36U may be provided between the central unit 32 and eachremote unit 34(1)-34(N) to carry uplink communications signals in apoint-to-point communications configuration.

As a further option, the downlink optical fiber 36D and uplink opticalfiber 36U could be provided as a single optical fiber (not shown) tocarry both downlink and uplink signals. Time-division multiplexing ofthe downlink and uplink signals may be employed to allow the downlinkand uplink signals to be communicated over a single optical fiber.Wave-division multiplexing (WDM), such as discussed in U.S. patentapplication Ser. No. 12/892,424 entitled “Providing Digital DataServices in Optical Fiber-based Distributed Radio Frequency (RF)Communications Systems, And Related Components and Methods,”incorporated herein by reference in its entirety, may also be employedin this scenario to prevent collisions between downlink and uplinkcommunications signals in the same or overlapping frequency bands.Further, U.S. patent application Ser. No. 12/892,424 also disclosesdistributed digital data communications signals in a distributed antennasystem which may also be distributed in the DAS 30 either in conjunctionwith RF communications signals or not.

With reference back to FIG. 2, the central unit 32 of the DAS 30 is alsoconfigured to distribute management signals between one or more sources,such as between a management controller 46, and the remote units34(1)-34(N). The management controller 46 may be a computer or consoleas non-limiting examples. For example, the management controller 46 maybe configured to provide management signals to perform a variety oftasks or applications. Examples of management signals that may bedistributed in the DAS 30 include configuration signals, controlsignals, gain control signals, monitoring signals, and configurationsignals, fault signals, and alarm signals. The management signals arenot for providing RF communications services between the base station(s)40 and the client devices 42(1)-42(N). The management signals may becommunicated according to any protocol desired, such as the Ethernetprotocol.

The central unit 32 is configured to receive downlink management signals44D from the management controller 46. The central unit 32 distributesthe downlink management signals 44D to the remote units 34(1)-34(N) tobe distributed to the client devices 42(1)-42(N) communicatively coupledto the remote units 34(1)-34(N). The management controller 46 providesdownlink management signals 44D to be distributed by the central unit 32to any number of remote units 34(1)-34(N). Thus, to prevent the downlinkmanagement signals 44D destined for different remote units 34(1)-34(N)from interfering with each other, the central unit 32 time-divisionmultiplexes the downlink electrical management signals 44D(E) intoindividual time slots in a downlink TDM management frame signal to bedistributed to the remote units 34(1)-34(N). The central unit 32converts the downlink TDM electrical management signal to downlink TDMoptical management signals 44D(0) to be distributed over the at leastone downlink optical fiber 36D to the remote units 34(1)-34(N) and theclient devices 42(1)-42(N) in this embodiment. The central unit 32 canbe configured to either broadcast all downlink electrical managementsignals 44D(E) to all remote units 34(1)-34(N), or provide specificdownlink electrical management signals 44D(E) to individual remote units34(1)-34(N).

In this embodiment, as will be described in more detail below, thedownlink TDM optical management signals 44D(0) are combined with thedownlink optical communications signals 38D(0) in different frequencybands and distributed over the same downlink optical fiber 36D. Theremote units 34(1)-34(N) are configured to receive and convert downlinkTDM optical management signals 44D(0) to downlink TDM electricalmanagement signals, which can then be parsed by each remote unit34(1)-34(N) to receive a particular downlink electrical managementsignal 44D(E) destined for the remote unit 34(1)-34(N).

The remote units 34(1)-34(N) are also configured to create and provideuplink management signals 44U to be distributed to the central unit 32and the management controller 46. For example, it may be desired for theremote units 34(1)-34(N) to have the ability to provide the same type ofmanagement signals described above to the central unit 32, which are notrelated to RF communications services provided to the base station(s)40. In this regard, uplink electrical management signals 44U(E) may beprovided by the client devices 42(1)-42(N) to the remote units34(1)-34(N). The remote units 34(1)-34(N) time-division multiplex theuplink electrical management signals 44U(E) into individual time slotsin an uplink TDM electrical management frame signal. Thus, themanagement signals received by the central unit 32 from different remoteunits 34(1)-34(N) do not interfere with each other. The remote units34(1)-34(N) combine the received uplink TDM electrical managementsignals with uplink electrical communications signals 38U(E), and arethen configured to convert the combined uplink TDM electrical managementsignals and uplink electrical communications signals 38U(E) to combineduplink TDM optical management signals 44U(0) and uplink opticalcommunications signals 38U(0) to be distributed over the at least oneuplink optical fiber 36U to the central unit 32.

With continuing reference to FIG. 2, the central unit 32 is configuredto convert the received combined uplink TDM optical management signals44U(0) and uplink optical communications signal 38U(0) into combineduplink TDM electrical management signals 44U(E) and uplink electricalcommunications signal 38U(E). The central unit 32 then splits the uplinkTDM electrical management signals 44U(E) from the uplink electricalcommunications signals 38U(E). The central unit 32 is configured totranslate the uplink TDM electrical management signals 44U(E) intoindividual uplink electrical management signals 48U(E) from thedifferent remote units 34(1)-34(N) and provide the uplink electricalmanagement signals 48U(E) to the management controller(s) 46.

With continuing reference to FIG. 2, the remote units 34(1)-34(N) in theDAS 30 are communicatively coupled to the client devices 42(1)-42(N) bya separate electrical RF communications medium 50 and an electricalmanagement communications medium 52. In this embodiment, the electricalRF communications medium 50 includes a separate downlink electrical RFcommunications medium 50D and an uplink electrical RF communicationsmedium 50U. Alternatively, the downlink electrical RF communicationsmedium 50D and uplink electrical RF communications medium 50U may beprovided as a single electrical RF communications medium that carriesboth downlink and uplink RF communications signals. The electricalmanagement communications medium 52 in FIG. 2 also includes a separatedownlink electrical management communications medium 52D and an uplinkelectrical management communications medium 52U. Alternatively, thedownlink electrical management communications medium 52D and the uplinkelectrical management communications medium 52U may be provided as asingle electrical management communications medium that carries bothdownlink and uplink management communications signals. The electricalmanagement communications mediums 50, 52 may be coaxial cables, forexample.

In the present embodiments, the downlink optical fiber 36D and uplinkoptical fiber 36U could be provided as a single optical fiber to carrycombined downlink optical communications signals 38D(0), downlinkelectrical TDM management frame signals 44D(0), uplink TDM opticalmanagement signals 44U(0), and uplink optical communications signals38U(0). Time-division multiplexing of the downlink and uplink signalsmay be employed to allow these downlink and uplink signals to becommunicated over a single optical fiber. Wave-division multiplexing(WDM), such as discussed in U.S. patent application Ser. No. 12/892,424,incorporated herein by reference in its entirety, may also be employedin this scenario to prevent collisions between downlink and uplinkcommunications signals in the same or overlapping frequency bands.

FIG. 3 illustrates a control circuit 60 used to control toggling betweentransmit and receive mode in a system, such as a DAS, supportingtime-division duplexing (TDD). The control circuit 60 can be used with,for example, distributed antenna systems, repeaters, and other hardwareand architectures that provide wireless services. The control circuit 60can be interposed, for example, between a radio source, such as a basestation, and head end equipment of a distributed antenna system. Thecontrol circuit 60 can also be integrated into one or more components ofa distributed antenna system, including head end equipment. For thepurposes of illustration, the control circuit 60 is described below inthe context of a distributed antenna system, although otherimplementations will be recognized by those of skill in the art. Thecontrol circuit 60 can include, or can be coupled to, a TDD switchingcircuit 64.

Still referring to FIG. 3, the control circuit 60 in this example isprovided in a distributed communications system in the form of a DAS 61in this example. The control circuit 60 includes a directional coupler76 and two power detectors 80, 82. The transmit (Tx) power detector 80measures Tx power, in decibels (dB), arriving in the downlink directionon a downlink path 83D, such as from the radio source 10, which is anindication of the power level received in the downlink direction on adownlink path 83D. The receive (Rx) power detector 82 measures Rx power,in dBm, generated by a Receive (Rx) amplifier 86, which is an indicationof the power level received in the uplink direction on an uplink path83U. Power received ‘from the uplink direction’ on the uplink path 83Ucan come from a system serviced by the radio source 10, such as from aDAS or a repeater. The decision by the control circuit 60 to togglebetween the TDD Tx mode and TDD Rx mode is based on a comparison of thepower level received from the radio source 10 and the power levelreceived from the DAS 61. The Tx power detector 80 and the Rx powerdetector 82 may be provided in the form of diodes, as a non-limitingexample.

The Tx/Rx comparator 90 makes the determination of whether the Tx powerfrom the radio source 10 in the downlink path 83D is higher than the Rxpower in the uplink path 83U. A Tx power higher than Rx power is onecondition for toggling the TDD transmission mode to TDD Tx mode. In thisexample, the default TDD transmission mode for the control circuit 60 isTDD Rx mode, and a Tx power in excess of Rx power does not necessarilytoggle the TDD transmission mode from TDD Rx mode to TDD Tx mode. Txpower can also be required to exceed a minimum threshold value to effecta switching, which is determined by a Transmit (Tx) power comparator100. The threshold value can be variable and established to a desiredlevel by a Tx power reference 102. A digital-to-analog converter (DAC)103 may be included to convert the Tx power reference 102 from a digitalsignal to an analog signal if the Tx power comparator 100 is an analogcomparator.

A Tx saturation comparator 108 compares the detected Tx power to asaturation level reference 110. A digital-to-analog converter (DAC) 111may be included to convert the saturation level reference 110 from adigital signal to an analog signal if the Tx saturation comparator 108is an analog comparator. The Tx saturation comparator 108 addressessituations in which the Tx power detector 80 is saturated due to high Txpower, and as a result the power levels measured by Tx power detector 80and the Rx power detector 82 might be seen as equal. This conditionmight cause an error in toggling from TDD Tx mode to TDD Rx mode, orvice versa. If the output of the Tx saturation comparator 108 is “1”,the assumption is that the Tx power detector 80 is saturated due to highpower arriving from the radio source. In this case, the logic circuit120 decides that the DAS should be toggled to TDD Tx mode.

The Rx amplifier 86, an input switch 130, an antenna switch 134, and aTransmit (Tx) amplifier 138 are illustrated as forming the TDD switchingcircuit 64 to effect the TDD Tx mode and TDD Rx mode in the system.Based on the state of the three comparators 90, 100, 108, the logic 120decides if the switching circuit 64 will set the DAS to TDD Tx mode orTDD Rx mode. The logic circuit 120 schedules the toggling of the inputswitch 130 and the antenna switch 134. In order to avoid a situationwhere the antenna switch 134 is toggled under power when toggling fromTDD Rx mode to TDD Tx mode, the logic circuit 120 first toggles theantenna switch 134 and then the input switch 130.

The logic circuit 120 can have three states based on the outputs of thecomparators 90, 100, 108. A first state can correspond to when thereceive/transmit comparator 90 determines that Rx power exceeds Txpower. In the first state, the switching circuit 64 receives aninstruction through, for example, a digital control bit, “1” for TDD Txmode, and “0” for TDD Rx mode, to maintain the DAS in receive mode. Forexample, the instruction may be provided on a Tx/Rx sense output 122from the logic circuit 120. The logic circuit 120 may have more than oneTx/Rx sense output 122 if there is a need for other system in the DAS 61to be switched between TDD Tx mode and TDD Rx mode. The outputs of thecomparators 100, 108 are not relevant in this state. In the secondstate, the receive/transmit comparator 90 determines that Tx powerexceeds Rx power, but the Tx power comparator 100 determines that Txpower does not exceed the Tx power reference 102. In the second state,the TDD switching circuit 64 is instructed to operate the DAS in receivemode. In the third state, if the Tx power is higher than the Rx powerand the Tx power is higher than the Tx reference value, the TDDswitching circuit 64 is instructed to operate the DAS in transmit mode.If the output of the Tx saturation comparator 108 is “1”, indicatingthat the Tx power detector 80 is saturated due to high power arrivingfrom the radio source 10, the switching circuit 64 is instructed tooperate the DAS in transmit mode.

According to one aspect of the present embodiments, a simple and robustmechanism provides a simple and robust switching of a DAS, repeater, orsimilar component between TDD uplink (Rx) mode and TDD downlink (Tx)mode. The exemplary control circuit 60 uses simple components without aneed for an expensive high directivity directional coupler required byconventional schemes.

The digital reference 102 and the saturation level reference 110 may be,for example, digital words that can be set digitally by softwarecommands. The exemplary comparators are shown as comparators 90, 100,108, although other components might be used. The exemplary powerdetectors 80, 82 are illustrated as diodes, although other componentsmight be used.

The RF communications services supported by the distributed antennasystems disclosed in this application, such as the DAS 14, 30, or 61 mayinclude, but are not limited to, US FCC and Industry Canada frequencies(824-849 MHz on uplink and 869-894 MHz on downlink), US FCC and IndustryCanada frequencies (1850-1915 MHz on uplink and 1930-1995 MHz ondownlink), US FCC and Industry Canada frequencies (1710-1755 MHz onuplink and 2110-2155 MHz on downlink), US FCC frequencies (698-716 MHzand 776-787 MHz on uplink and 728-746 MHz on downlink), EU R & TTEfrequencies (880-915 MHz on uplink and 925-960 MHz on downlink), EU R &TTE frequencies (1710-1785 MHz on uplink and 1805-1880 MHz on downlink),EU R & TTE frequencies (1920-1980 MHz on uplink and 2110-2170 MHz ondownlink), US FCC frequencies (806-824 MHz on uplink and 851-869 MHz ondownlink), US FCC frequencies (896-901 MHz on uplink and 929-941 MHz ondownlink), US FCC frequencies (793-805 MHz on uplink and 763-775 MHz ondownlink), and US FCC frequencies (2495-2690 MHz on uplink anddownlink), medical telemetry frequencies, WLAN, WiMax, WiFi, DigitalSubscriber Line (DSL), and LTE, etc.

Any of the distributed communications systems and/or DAS componentsdisclosed herein, including but not limited to the control circuit 60 inFIG. 3, can include a computer system. For example, the logic circuit120 of the control circuit 60 in FIG. 3 may be implemented in a computersystem that includes a microprocessor or other controller that isconfigured to execute software to control the TDD transmission mode. Inthis regard, FIG. 4 is a schematic diagram representation of additionaldetail regarding an exemplary form of a computer system 140 that isadapted to execute instructions from a computer-readable medium toperform power management functions and can be included in a distributedantenna system component(s). The computer system 140 includes a set ofinstructions for causing the distributed antenna system component(s) toprovide its designed functionality. The DAS component(s) may beconnected (e.g., networked) to other machines in a LAN, an intranet, anextranet, or the Internet. The DAS component(s) may operate in aclient-server network environment, or as a peer machine in apeer-to-peer (or distributed) network environment. While only a singledevice is illustrated, the term “device” shall also include anycollection of devices that individually or jointly execute a set (ormultiple sets) of instructions to perform any one or more of themethodologies discussed herein. The DAS component(s) may be a circuit orcircuits included in an electronic board card, such as a printed circuitboard (PCB) as an example, a server, a personal computer, a desktopcomputer, a laptop computer, a personal digital assistant (PDA), acomputing pad, a mobile device, or any other device, and may represent,for example, a server or a user's computer. The exemplary computersystem 140 in this embodiment includes a processing device or processor142, a main memory 144 (e.g., read-only memory (ROM), flash memory,dynamic random access memory (DRAM) such as synchronous DRAM (SDRAM),etc.), and a static memory 146 (e.g., flash memory, static random accessmemory (SRAM), etc.), which may communicate with each other via the databus 148. Alternatively, the processing device 142 may be connected tothe main memory 144 and/or static memory 146 directly or via some otherconnectivity means. The processing device 142 may be a controller, andthe main memory 144 or static memory 146 may be any type of memory.

The processing device 142 represents one or more general-purposeprocessing devices such as a microprocessor, central processing unit, orthe like. More particularly, the processing device 142 may be a complexinstruction set computing (CISC) microprocessor, a reduced instructionset computing (RISC) microprocessor, a very long instruction word (VLIW)microprocessor, a processor implementing other instruction sets, orprocessors implementing a combination of instruction sets. Theprocessing device 142 is configured to execute processing logic ininstructions 162 for performing the operations and steps discussedherein.

The computer system 130 may further include a network interface device140. The computer system 130 also may or may not include an input 142 toreceive input and selections to be communicated to the computer system130 when executing instructions. The computer system 130 also may or maynot include an output 144, including but not limited to a display, avideo display unit (e.g., a liquid crystal display (LCD) or a cathoderay tube (CRT)), an alphanumeric input device (e.g., a keyboard), and/ora cursor control device (e.g., a mouse).

The computer system 140 may or may not include a data storage devicethat includes instructions 156 stored in a computer-readable medium 158.The instructions 156 may also reside, completely or at least partially,within the main memory 144 and/or within the processing device 142during execution thereof by the computer system 140, the main memory 144and the processing device 142 also constituting computer-readablemedium. The instructions 156 may further be transmitted or received overa network 160 via the network interface device 150.

While the computer-readable medium 158 is shown in an exemplaryembodiment to be a single medium, the term “computer-readable medium”should be taken to include a single medium or multiple media (e.g., acentralized or distributed database, and/or associated caches andservers) that store the one or more sets of instructions. The term“computer-readable medium” shall also be taken to include any mediumthat is capable of storing, encoding or carrying a set of instructionsfor execution by the processing device and that cause the processingdevice to perform any one or more of the methodologies of theembodiments disclosed herein. The term “computer-readable medium” shallaccordingly be taken to include, but not be limited to, solid-statememories, optical and magnetic medium, and carrier wave signals.

The embodiments disclosed herein include various steps. The steps of theembodiments disclosed herein may be performed by hardware components ormay be embodied in machine-executable instructions, which may be used tocause a general-purpose or special-purpose processor programmed with theinstructions to perform the steps. Alternatively, the steps may beperformed by a combination of hardware and software.

The embodiments disclosed herein may be provided as a computer programproduct, or software, that may include a machine-readable medium (orcomputer-readable medium) having stored thereon instructions, which maybe used to program a computer system (or other electronic devices) toperform a process according to the embodiments disclosed herein. Amachine-readable medium includes any mechanism for storing ortransmitting information in a form readable by a machine (e.g., acomputer). For example, a machine-readable medium includes amachine-readable storage medium (e.g., read only memory (“ROM”), randomaccess memory (“RAM”), magnetic disk storage medium, optical storagemedium, flash memory devices, etc.).

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein may be implementedor performed with a processor, a Digital Signal Processor (DSP), anApplication Specific Integrated Circuit (ASIC), a Field ProgrammableGate Array (FPGA) or other programmable logic device, discrete gate ortransistor logic, discrete hardware components, or any combinationthereof designed to perform the functions described herein. A controllermay be a processor. A processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The embodiments disclosed herein may be embodied in hardware and ininstructions that are stored in hardware, and may reside, for example,in Random Access Memory (RAM), flash memory, Read Only Memory (ROM),Electrically Programmable ROM (EPROM), Electrically ErasableProgrammable ROM (EEPROM), registers, a hard disk, a removable disk, aCD-ROM, or any other form of computer-readable medium known in the art.Storage media may be coupled to the processor such that the processorcan read information from, and write information to, the storage medium,or integral to the processor. The processor and the storage medium mayreside in an ASIC. The ASIC may reside in a remote station as discretecomponents in a remote station, base station, or server.

As used herein, the terms “fiber optic cables” and/or “optical fibers”include all types of single mode and multi-mode light waveguides,including one or more optical fibers that may be upcoated, colored,buffered, ribbonized and/or have other organizing or protectivestructure in a cable such as one or more tubes, strength members,jackets or the like. The optical fibers disclosed herein can be singlemode or multi-mode optical fibers.

We claim:
 1. A communication system capable of supporting time-divisionduplexing (TDD), the communication system comprising: a central unitconfigured to receive a plurality of downlink signals; at least oneremote unit configured to receive downlink signals from the centralunit, and to return uplink signals to the central unit; and a controlcircuit for controlling TDD switching in the communication system, thecontrol circuit comprising: a first power detector configured todetermine a first power level; a second power detector configured todetermine a second power level from an uplink path; a receive/transmitcomparator coupled to the first power detector and to the second powerdetector, wherein the receive/transmit comparator compares the firstpower level to the second power level to provide an indicationindicating when the first power level exceeds the second power level;and a transmit power comparator configured to determine whether thefirst power level exceeds a reference value and provide an indicationindicative of whether the first power level exceeds the reference value,wherein the control circuit is configured to determine if thecommunication system should be switched to TDD transmit mode or TDDreceive mode based at least in part on the received indication from thereceive/transmit comparator and the received indication from thetransmit power comparator; and a TDD switching circuit configured toeffect the TDD transmit mode and a TDD receive mode for thecommunication system, the TDD switching circuit comprising an inputswitch and an antenna switch located between the input switch and thecommunication system.
 2. The communication system of claim 1, furthercomprising a saturation comparator configured to compare the first powerlevel with a saturation level reference and provide an indication ofsaturation of the first power detector, wherein the control circuit isconfigured to receive the indication of saturation and determine if thesystem should be switched to TDD transmit mode or TDD receive mode basedat least in part on the received indication of saturation from thesaturation comparator.
 3. The communication system of claim 1, whereinthe TDD switching circuit further comprises a transmit amplifier and areceive amplifier located between the input switch and the antennaswitch.
 4. The communication system of claim 3, wherein the input switchand the antenna switch are configured to operate in coordination toeffect the TDD transmit mode and the TDD receive mode.
 5. Thecommunication system of claim 3, further comprising a directionalcoupler configured to receive and transmit communications between theTDD switching circuit, at least one radio source, the first powerdetector, and the second power detector.
 6. The communication system ofclaim 1, wherein the central unit further comprises at least oneelectrical-to-optical converter configured to convert downlinkelectrical signals from at least one radio source to downlink opticalsignals, and wherein the at least one remote unit is configured totransmit wireless communications into a coverage area and receivewireless communications from client devices in a coverage area.
 7. Acommunication system capable of supporting time-division duplexing(TDD), the communication system comprising: a unit configured to receivea plurality of downlink signals; a plurality of remote units coupled tothe unit by an optical fiber infrastructure, each remote unit configuredto receive optical downlink signals from the unit, and to return opticaluplink signals to the unit; and a control circuit for controlling TDDswitching in the communication system, the control circuit comprising: afirst power detector configured to determine a first power level; asecond power detector configured to determine a second power level froman uplink path; a receive/transmit comparator coupled to the first powerdetector and to the second power detector, wherein the receive/transmitcomparator compares the first power level to the second power level toprovide an indication indicating when the first power level exceeds thesecond power level; and a transmit power comparator configured todetermine whether the first power level exceeds a reference value andprovide an indication indicative of whether the first power levelexceeds the reference value, wherein the control circuit is configuredto determine if the communication system should be switched to TDDtransmit mode or TDD receive mode based at least in part on the receivedindication from the receive/transmit comparator and the receivedindication from the transmit power comparator.
 8. The communicationsystem of claim 7, wherein the unit further comprises at least oneelectrical-to-optical converter configured to convert downlinkelectrical signals from at least one radio source to downlink opticalsignals, and wherein the plurality of remote units are each configuredto transmit wireless communications into a coverage area and receivewireless communications from client devices in a coverage area.
 9. Thecommunication system of claim 8, further comprising a saturationcomparator configured to compare the first power level with a saturationlevel reference and provide an indication of saturation of the firstpower detector.
 10. The communication system of claim 9, wherein thecontrol circuit is configured to receive the indication of saturationand determine if the system should be switched to TDD transmit mode orTDD receive mode based at least in part on the received indication ofsaturation from the saturation comparator.
 11. The communication systemof claim 8, further comprising a TDD switching circuit configured toeffect the TDD transmit mode and a TDD receive mode for thecommunication system, the TDD switching circuit comprising: an inputswitch and an antenna switch; and a transmit amplifier and a receiveamplifier located between the input switch and the antenna switch.
 12. Acommunication system capable of supporting time-division duplexing(TDD), the communication system comprising: a unit configured to receivea plurality of downlink signals; a plurality of remote units eachconfigured to receive downlink signals from the unit and to returnuplink signals to the unit, each remote unit comprising at least oneelectrical-to-optical converter and being configured to transmitwireless communications into a coverage area and receive wirelesscommunications from client devices in a coverage area; and a controlcircuit for controlling TDD switching in the communication system, thecontrol circuit comprising: a first power detector configured todetermine a first power level; a second power detector configured todetermine a second power level from an uplink path; a receive/transmitcomparator coupled to the first power detector and to the second powerdetector, wherein the receive/transmit comparator compares the firstpower level to the second power level to provide an indicationindicating when the first power level exceeds the second power level;and a transmit power comparator configured to determine whether thefirst power level exceeds a reference value and provide an indicationindicative of whether the first power level exceeds the reference value,wherein the control circuit is configured to determine if thecommunication system should be switched to TDD transmit mode or TDDreceive mode based at least in part on the received indication from thereceive/transmit comparator.
 13. The communication system of claim 12,further comprising a TDD switching circuit configured to effect the TDDtransmit mode and a TDD receive mode for the communication system. 14.The communication system of claim 13, wherein the control circuit isconfigured to determine if the distributed communication system shouldbe switched to TDD transmit mode or TDD receive mode based at least inpart on the received indication from the transmit power comparator. 15.The communication system of claim 13, wherein the TDD switching circuitcomprises: an input switch and an antenna switch located between theinput switch and the communication system; and a transmit amplifier anda receive amplifier located between the input switch and the antennaswitch.
 16. The communication system of claim 15, further comprising asaturation comparator configured to compare the first power level with asaturation level reference and provide an indication of saturation ofthe first power detector, wherein the control circuit is configured toreceive the indication of saturation and determine if the system shouldbe switched to TDD transmit mode or TDD receive mode based at least inpart on the received indication of saturation from the saturationcomparator.
 17. The communication system of claim 16, wherein the firstpower detector comprises a diode, the second power detector comprises adiode, and wherein the receive/transmit comparator, the transmit powercomparator, and the saturation comparator have as an input an output ofthe first power detector.